The present invention relates generally to industrial lubricants. More specifically the invention relates to industrial gear oils for service in cold temperature operations.
The art of lubricating oil formulation has become increasingly complex with ever more stringent standards dictated by developing industrial equipment technology. For example, industrial gear oils are needed for service over a wide range of climate conditions. To meet cold temperature service conditions the lubricant must have a low pour point and a low viscosity. Low pour points and low viscosity can be achieved using a basestock that contains a substantial amount of a very light naphthenic oil.
Another requirement of industrial gear oils is that they be capable of demulsifying water which often contaminates the gear oil under conditions of use. Unfortunately, naphthenic oils used in gear oil products are readily emulsified.
In addition to the low temperature and demulsification properties, industrial oils need to protect the lubricated parts against extreme pressure. Consequently, industrial oils such as gear oils are formulated to contain extreme pressure additive systems. Thus, typically they include a dispersant to prevent gearbox sludge deposits. The dispersants, however, tends to be effective in emulsifying low viscosity naphthenic oils.
An object of the present invention therefore is to provide an industrial lubricant that is has good low temperature properties and that is capable of demulsifying water.
According to the invention, a lubricant composition especially useful as a gear oil, comprises:
(a) a base oil consisting essentially of a mixture of
(i) at least about 10 wt % based on the total weight of the composition of one or more naphthenic oils having a viscosity in the range of in the range of about 6 to about 80 cSt at 40xc2x0 C.;
(ii) about 10 to about 90 wt % based on the weight of the composition of a mineral oil having a viscosity in the range of about 100 to about 500 cSt at 40xc2x0 C.; and
(b) an effective amount of a demulsification additive selected from the group consisting of oxyalkylated glycols, esters of oxyalkylated glycols and mixtures thereof.
Other embodiments of the invention will become apparent from the detailed description which follows:
A. The Base Oil
The lubricant compositions of the present invention are especially useful as gear oils and comprise a major amount of a base oil which consists essentially of a mixture of a naphthenic oil and a mineral oil.
(i) The Naphthenic Oil
The naphthenic oil used in the base oil may be selected from one or more naphthenic oils having a viscosity in the range of about 6 to about 80 cSt at 40xc2x0 C. and preferably in the range of 6 to 20 cSt at 40xc2x0 C. The naphthenic oil or oils will comprise at least about 10 wt % of the total weight of the composition, for example from about 10 to about 70 wt %.
(ii) The Mineral Oil
The mineral oil used in the base oil may be selected from any of the natural mineral oils of API Groups I, II, III or mixtures of these having a viscosity in the range of about 100 to about 500 cSt at 40xc2x0 C. Especially preferred are solvent extracted bright stocks having a viscosity in the range of 350 to 500 cSt at 40xc2x0 C.
B. The demulsification Additive
The lubricant compositions also includes an effective amount of a demulsification additive selected from the group consisting of oxyalkylated glycols, esters of oxyalkylated glycols and mixtures thereof Typically the glycols will have from 2 to 10 carbon atoms and preferably 2 carbon atoms. Also the alkylene groups of the oxyalkylates may have from 2 to about 10 carbon atoms although the oxyalkylate preferably are oxyethylene, oxypropylene, and mixtures of oxyethylene and oxypropylene groups. The oxyalkylated esters preferably are derived from glycols of from 2 to about 20 carbon atoms and dibasic acids and acid anhydrides having from about 2 to 10 carbon atoms, especially maleic acid or anhydride. Suitable oxyalkylated glycols and esters of oxyalkylated glycols typically have molecular weights in excess of about 50,000, for example in the range of about 100,000 to about 500,000, and even higher. Such demulsification additives are commercially available materials.
Typically the demulsification additives will comprise from about 0.002 to about 0.04 wt % of the composition and preferably about 0.02 to about 0.03 wt %.
C. Other Additives
The composition of the present invention may include other additives such as extreme pressure agents, metal deactivators, antioxidants, rust inhibitors, pour point depressants, dispersants, and antifoamants.
Among suitable extreme pressure agents are olefin polysulfides and phosphate esters.
For antioxidants hindered phenols and alkylated diphenyl amines are especially useful.
Benzotriazole derivatives are useful in the lubricant composition as a metal passivator.
Polymethylacrylates exemplify useful pour point depressants.
Alkyl succinimides may be used as antitrust additives.
Among suitable dispersants mention is made of polyisobutylene succinic anhydride polyamine.
The antifoamant used typically will be a silicone oil antifoamant.
The foregoing additives are all commercially available materials. Indeed, these additives are usually not added independently but are precombined in packages which can be obtained from suppliers of lube oil additives. Additive packages with a variety of ingredients, proportions and characteristics are available and selection of the appropriate package will take the requisite use of the ultimate composition into account.